A fine circuit pattern is produced on a surface of a semiconductor wafer or glass substrate by a photolithographic step and an etching step. In the photolithographic step, a chemical liquid supplying apparatus is used to apply the chemical liquid such as photoresist liquid onto the surface of the wafer or glass substrate. By doing so, the chemical liquid accommodated in a container is sucked up by a pump, passes through a filter etc., and is applied from a nozzle onto a material to be applied such as a wafer. When particles such as dusts have been mixed in the chemical liquid to be applied, they adhere to the material to be applied, thereby causing pattern defects and resulting in lowering a yield of products. If the chemical liquid stays in the pump for a long term, it changes in quality. Therefore, since the chemical liquid changed in quality becomes particles in some cases, it is required that there is no chemical liquid accumulation in the pump for discharging the chemical liquid.
As the pump for discharging the chemical liquid, there is used such a pump that an expansion/contraction chamber in which the chemical liquid flows and a pump chamber are partitioned from each other by an elastically deformable partition membrane such as an diaphragm, tube, or the like. By doing so, the pump chamber is filled with indirect liquid, namely, an incompressible medium, and the chemical liquid is pressurized through the partition membrane. A pressurizing system for the incompressible medium includes a bellows-type system as described in Japanese patent application laid-open publication No. 10-61558 and a syringe-type system using a piston as described in U.S. Pat. No. 5,167,837.
When the diaphragm or tube is elastically deformed by the incompressible medium to perform a pumping operation, the accumulation of the chemical liquid can be prevented in the expansion/contraction chamber of the pump, and generation of the particles due to the accumulation of the chemical liquid can be prevented. To the contrary, the incompressible medium serves as an important factor for determining performance of the pump. That is, when air enters into the incompressible medium from the outside, incompressibility of the incompressible medium is macroscopically lost, so that movement of the bellows or piston cannot be faithfully transmitted to the diaphragm or tube, and a movement stroke of the bellows or piston results in not corresponding to a discharge amount of chemical liquid. Similarly thereto, even when the incompressible medium leaks, the movement stroke of the bellows or the like results in not corresponding to the discharge amount of chemical liquid, so that the chemical liquid cannot be discharged with high accuracy.
In the syringe-type pump described above, a cylinder is generally provided with a seal member contacting with an outer peripheral face of the piston so that a region between an interior of the a driving chamber on a tip face side of the piston and the outside on a basal end face side of the piston is sealed. At this time, the piston regards the seal member as a boundary and reciprocates between a portion accommodating the incompressible medium and the outside. Therefore, in some cases, the piston may be exposed to the outside in a state where the incompressible medium adheres to an outer peripheral face of the piston. The adhered incompressible medium becomes a thin-film shape to enter into a region between the outer peripheral face and the seal member, and so serves as lubricant for avoiding direct contact between the seal member and the outer peripheral face of the piston. To the contrary, a portion of the incompressible medium exposed to the outside evaporates or dries little by little, thereby disappearing from a surface of the piston and resulting in decreasing an amount of incompressible medium. Further, when the incompressible medium exposed to the outside vaporizes, the incompressible medium functioning as lubricant disappears from the outer peripheral face of the piston, thereby becoming in a state of lacking an oil film. Therefore, since the seal member directly contacts with the outer peripheral face of the piston, frictional wear of the seal member progresses.
When the piston is moved backward in order to expand the pump chamber partitioned by the partition membrane and suck the chemical liquid contained in the container into the pump chamber, the incompressible medium becomes in a negative pressure state, so that external ambient air may enter into the incompressible medium from a region between the outer peripheral face of the piston and an inner peripheral face of the cylinder. This phenomenon becomes significant when a sealing property lowers due to the frictional wear of the seal member slidably contacting with the outer peripheral face of the piston. Also, the same phenomenon occurs even when large negative pressure is applied to the incompressible medium by the piston.
In contrast, in the bellows-type pump as described above, since a seal member contacting with a sliding face is not used, there is an advantage of a high airtight property of the pump chamber or driving chamber filled with the incompressible medium. However, pressure applied to the incompressible medium in the bellows-type pump is lower than that in the syringe-type pump. For example, when a resist is discharged to the nozzle through a filter, pressure in the pump chamber becomes high due to high flow resistance in the filter. When the bellow is driven, pressure of the incompressible medium becomes high and the bellows may slightly expand or contact. Therefore, when the bellows are slightly expands or contracts, the movement stroke of the bellows results in not corresponding to the discharge amount of chemical liquid with high accuracy.
An object of the present invention is to provide a chemical liquid supplying apparatus that can discharge the chemical liquid with high accuracy.
Another object of the present invention is to provide a chemical liquid supplying apparatus that can prevent the incompressible medium from leaking from a region between the piston and the cylinder.
Still another object of the present invention is to provide a chemical liquid supplying apparatus in which a lubricating property of the seal member can be improved by interposing a film of the incompressible medium in the seal member for sealing the region between the piston and the cylinder.